Thermal responsive circuit controller



F 1944- s. M. HAUSLER 2,340,377

THERMAL RESPONSIVE CIRCUIT CONTROLLER Filed larch 12, 1943 Ml-llllllllllllak: 1h

Inventor'- Ge orge M. Hauslen y H i s Attorggg/ 'atented Feb. 8, 1944 THERMAL RESPONSIVE cmoorr CONTROLLER George M. Hausler, Ballston Lake, N. Y., assignor to General Electric Company,

New York a corporation of Application March 12, 1943, Serial No. 478L928 8 Claims. (Cl. 200-113) My invention relates to thermal responsive circuit controllers and particularly to hot wire relays of the type having contacts, normally biased toward a circuit closing position.

Hot wire relays of the normally open type commonly comprise a contact member which is normally biased to a circuit closing position in combination with a thermally expansible wire arranged normally to exert a tensile force to hold the switch member in a circuit opening position against its bias when the wire is cooled and contracted. With such an arrangement where the expansible wire is constantly under tension any mechanical failure, such as due to burn out of the wire, will ordinarily permit the contacts to close and remain closed so that other apparatus, such as a tripping relay energized thereby, may become overloaded. To provide fail safe operation of such a relay it is necessary to arrange the relay so that upon mechanical failure of the tension wire the contacts will assume an open circuit rather than a closed circuit position. It will be evident from the foregoing that by a normally open relay for the purpose of this application I mean one which is in a circuit opening position when deenergized, in that the relay is biased closed and held open by a normally deenergized element.

Accordingly, it is a general object of my invention to provide a snap action hot wire relay of the normally open type which shall assume a circuit opening position upon mechanical failure of the hot wire.

My invention also has for its object the provision. of a snap action hot wire relay biased to a circuit closing position and arranged to assume a circuit opening position upon mechanical failure of the hot wire.

In carrying out my invention in one form I provide an over-center snap acting switch member mounted upon a reciprocable actuating memher and cooperable with suitable stop means for effecting overcenter movement of the snap action switch member upon movement of the actuating member. Within a predetermined normal range of movement of the actuating member overcenter movement of the switch member is effective to engage and disengage a pair of switch contacts. The switch actuating member is biased toward a position to produce circuit closing overcenter movement of the switch member and into continuous following engagement with a thermally expansible linkage arranged normally to oppose the bias of the actuating member and to restrict movement of the actuating member to its predeinner ends of the arms termined normal range of movement. By reason of the overcenter arrangement snapping movement of the contacts is in a direction opposite to the initiating overcenter movement of the actuating member, so that the normal circuit closing bias upon the switch actuating member is in a direction tending to move the actuating member away from the stationary contact. In order to provide for positive circuit opening operation upon mechanical failure of the hot wire and release of the actuating member, the switch actuating member is arranged to move freely under the influence of its bias to a circuit open ing position beyond its predetermined normal range of movement and to carry with it the overcenter switch member, the switch member being thereby moved to such a position that overcenter movement of the switch member is ineffective to engage the contacts.

My invention itself will be better understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. 1 is a front view of a thermal responsive circuit controller embodying my invention, the snap action switch element being shown with the cover removed; Fig. 2 is a. plan View, partly in section, of the snap action switch element shown in Fig. 1; Fig. 3 is a fragmentary diagram of the controller of Fig. 1 showing the switch element in its circuit closing position; Fig. 4 is a view similar to that of Fig. 3 showing the switch element in its fail-safe position; and Fig. 5 is a perspective view of the switch actuating member forming part of the snap action switch of Figs. 1 to 4, inclusive.

Referring now to the drawing, I have shown my invention applied to a snap action switch of the type described and claimed in my copending application, S. N. 435,220, filed March 18, 1942, and assigned to the same assignee as the instant application. The switch is mounted in a casing l0 which is preferably made of an insulating compound molded to a suitable configuration and is provided with an insulating cover Illa. The switch member itself is formed of a unitary flat strip of spring material ll slotted at l2 and I3 to provide a pair of outer tension arms I4 and I5 and a central pair of opposing compression arms l6 and I1. The arms l6 and H are slightly deformable in compression and are formed by dividing a single central arm transversely in the .region of its center so that the IS and H are juxtaposed tacts I3 and I3 for engagement with the mov-' able contacts to limit their movement in opposite direction longitudinally of a reciprocable actuating and supporting member 30, 3| 32. The pair of flxed contacts 20 is arranged for engagement with the movable contacts I8 and I 3 in one position of equilibrium of the spring strip I I and the fixed stops 2| are arranged for engagement with the contacts I8 and I9 in the other position of equilibrium of the spring strip II.

The juxtaposed inner ends of the compression arms I3 and I! are pivotally mounted upon the slidable rod or shank portion 30 of the actuating member thereby to support the spring strip II upon the rod 30. The actuating'rod 30 itself is slidably supported in the casing III for movement of the pivoted inner ends of the compression arms I 3 and I I overcenter with respect to the plane of the spring strip II. The slidable rod 33 is shown provided with a pushbutton head portion 3| extending through a suitable aperture in the casing I0. Preferably, the actuating member also comprises the pair of bowed spring strips 32 clamped between the actuating rod 30 and the pushbutton head 3|. The spring strips 32 are provided with slightly curved base sections 33 arranged for insertion in suitable slots in the pushbutton head portion 3| in clamping relation betweenthe rod 30 and head portion 3|. The sections 33 of the springs 32 serve frictionally to attach the pushbutton head 3| to the slidable actuating rod 33 and to attach the spring strips 32 to the actuating member. Each of the spring strips 32 is notched at its lower end, as at 34, pivotally to support one of the juxtaposed inner ends of the deformable compression members I3 and I I. The springs 32 are biased outwardly to apply endwise forces to the members I3 and Il thereby to bend and spread the members I6 and I1 and to force their inner ends out of the plane of the spring strip II into alternative positions of equilibrium on opposite sides of the strip. The notched ends of the springs 32 provide a pivotal supporting and actuating connection between the actuating member 30, 3|, 32 and the resilient switch member II.

The normal spacing between the pivotal notches 34 in the actuating member is greater than the space between the juxtaposed inner ends of the members I3 and I! in the plane of the spring strip I I. It will, of course, be understood that if desired the springs 32 may be made integral, as in the form of a resilient yoke bridging the gap between the juxtaposed inner ends of the compression members l3 and I1.

The reciprocable actuating rod 30 is preferably biased to the position shown in Fig. 3 by means of a compression spring 35, one end of which engages a fixed stop 38 and the other end of which engages a shoulder 31 formed upon the actuating rod 33. Upward movement of the actuating rod 30 against the bias of the sprin 35 is limited only by the limit of compression of the spring. If desired, however, a suitable stop may be provided on the casing I for cooperation with a shoulder on the rod to limit upward movement of the rod to the position shown at Fig. 1. Downward movement of the actuating rod 30 under the influence of its bias may be limited only by engagement of the movable contacts I3 and I3 with the flxed stop 2| but is preferabi limited in a more positive manner by providin a peripheral flange or shoulder 33 upon the push .button head II for engagement with a portio of the casing I 3 in the manner shown at Fig. I In moving to the position shown in Pig. the actuating rod 33 carries with it the entir switch member II and thereby moves the switc' member to such a position remote from the flxe contacts that overcenter movement'of switcl member is ineifective to bring the movable con tacts into engagement with the stationary con tacts 20. To insure positive movement of th switch member to the position the actuatim rod 30 is provided with a pair of projecting de tents 40 arranged upon downward movemen of the rod to engage the outer tension arms I and I5 of the spring strip II and forcibly t4 move the entire spring strip to the position 0 Fig. 4 wherein the contacts are separated inde pendently of the overcenter position of the com pression arms I3 and I I.

To arrange the snap action switch describet above for operation in accordance with the temperature of a thermally expansible wire, I pro vide an operating lever 4| pivotally mounted a a fixed point 42 and arranged to engage the pushbutton head 3I. A thermally expansible wire 4| is connected between the operating lever 4| and a fixed point and is so arranged that wher cooled and contracted it exerts a tensile force tc hold the operating lever 4| in'engagement with the actuating member 33, 3|, 32 and to retain the actuating member 30 against its bias in the circuit opening position shown at Fig. 1. While the manner of connection of the expansible wire 43 is obviously not an essential part of my invention, the wire 43 is shown at Fig. l looped about a pulley 44 attached to the lever 4| with the ends ofthe wire connected to flxed contact terminals 45 and 48.

From the foregoing detailed explanation of the structure and arrangement of my circuitcontroller its mode of operation will be clear from the following brief description.

Assuming first that only a relatively small current is passing through the expansible wire 43, the wire is relatively cool and contracted, the operating lever 4| is drawn upward and the actuatingmember 30 is held against its bias in its upper or circuit opening position as shown at Fig. 1. If new the current passing through the wire 43 becomes greater, the wire expands and elongates and permits the operating lever 4| and the switch actuating member 30, 3|, 32 to move downwardly under the influence of the biasing spring 35. In the course of such downward movement the actuating member 30 car ries the pivoted inner ends of the compression members I3 and I1 overcenter with respect to the plane of the spring strip I I. As soon as such and I3 and the spring strip II effects a circuit control operation which precludes further excessive heating of the expansible wire 43. The wire 43 thereupon begins to cool and again contracts so that the operating lever 4| and the actuating member 30, 3|, 32 are again drawn upwardly to the position shown at Fig. 1. Connected in this manner the relay may also be used for sign flashing and the like.

As indicated at Fig. 3, the closed circuit position or" the actuating member 30, 3 I, 32 at which downward overcenter movement of the compression members [6 and I1 is effected is intermediate the extreme upper position shown in Fig. 1 and the extreme lower or fail safe" position of Fig. 4. The position of the actuating rod 30 in which downward overcenter movement of the compression members I6 and I1 takes place to effect upward circuit closing moving of the contact members is determined by the location of the fixed stops 2|. By suitable positioning of the stops the switch is so arranged that overcenter circuit closing movement upon downward movement of the actuating rod 30 occurs at a position intermediate the limiting positions shown at Figs. 1 and 4. Thus the positions of the actuating rod 30 shown at Figs. 1 and 3 define a normal range of movement of the actuating member between circuit opening and circuit closing positions in which overcenter movement of the switch member II is effective to engage and disengage the contacts.

Let it now be assumed that the wire 43 is burned out or otherwise mechanically fractured so that it no longer exerts a tensile force tending to draw the operating lever 43 upward against the bias of the spring 35. The pring 35 is now free to move the actuating member 30, 3|, 32 downwardly to the limit of its movement where the peripheral flange 38 on the push button head 3| engages the casing 10. In this downward movement the projecting detents 40 on the actuating lever 40 engage the outer tension arms I4 and of the spring strip ll thereby to ensure that the entire spring strip is carried downwardly with the actuating rod to a position of contact disengagement as shown at Fig. 4 where overcenter movement of the compression arm IE and I1 is ineifective to bring the movable contacts l8 and 19 into engagement with the fixed contacts 20. As shown at Fig. 4 the spring strip II is in its switch closing position in that the pivoted ends I of the compression arm l6 and H are below the plane of the spring strip. However, the entire spring strip is now so far removed from the stationary contacts 20 that even the circuit closing positioning of the spring strip itself would be ineffective to bring the switch contacts into engagement.

From the foregoing description of the operation of my relay it will be evident that it may also be advantageously used as a shunt relay to keep a motor or other electric translating device connected to a line only when the line voltage is between predetermined limits, for example to of normal voltage. For such use the wire 43 is connected across the line and the contacts 20 are connected in series with the translating'device to connect the device across the line in parallel with the wire 43. If new the line voltage is below 85% normal the wire is sufficiently cooled and contracted to keep the contacts I8, 20 and I9, 20 separated as shown at Fig. 1. When the line voltage is between 85% and 110% normal the wire 43 is expanded and the switch contacts closed to connect the electric translating device to the line. But if the line voltage exceeds 110% normal the wire 43 will burn out and. the switch will assume its "tail safe" position of Fig. 4 thereby to disconnect the translating device.

While I have shown only a preferred embodiment of my invention by way of illustration many modifications will undoubtedly occur to those skilled in the art and I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A thermal responsive circuit controller comprising a pair of cooperating switch contacts, an over-center switch member for controlling said contacts, a switch actuating member movable between circuit opening and circuit closing positions to eiiect over-center movement of said switch member, means for biasing said actuating member toward said circuit closing position, and thermally expansible member normally engaging said switch actuating member and opposing its bias to control movement of said actuating member between said positions, said biasing means being arrangedupon mechanical failure of said thermally expansible member positively to move said switch member and said actuating member to a circuit opening position independently of overcenter movement of said switch member.

2. A normally open thermal responsive circuit controller comprising a pair of cooperating switch contacts, a switch actuating member movable between two limiting switch opening positions through an intermediate switch closing position, means for biasing said switch actuating member to a first of said switch opening positions, an over-center switch member carried by said switch actuating member to control said contacts, fixed stop means operable in conjunction with said switch member to move said switch member hetween circuit opening and circuit closing positions as said actuating member is moved between the other of said switch opening positions ,and said intermediate position respectively, and

thermally expansible means for normally opposing the bias of said switch actuating member and limiting movement of said actuating member to a range between said second switch opening position and said intermediate position, said thermally expansible member being arranged when deenergized to hold said actuating member in said second switch opening position.

3. A thermal responsive circuit controller comprising a pair of cooperating switch contacts, a movable switch actuating member, an overcenter switch member supported upon said switch actuating member and arranged to control said contacts, fixed stop means operable in conjunction with said switch member upon movement of said actuating member within a predetermined normal range of movement to effect overcenter operation of said switch member between circuit opening and circuit closing positions, means for biasing said switch actuating member to a posi tion beyond said normal range of movement, said switch actuating member in moving to said position carrying said switch member to a position of contact disengagement independently of the overcenter position of said switch member, and thermally expansible means for normally opposing the bias of said actuating member and controlling movement of said member within said normal range in accordance with the temperature of said expansible member.

4. A thermal responsive circuit controller comprising a fixed contact, an over-center switch member ca rying a movable contact for cooperation with said fixed contact, a movable switch actuating member for supporting said switch member, stop means including said fixed contacts and operable in conjunction with said switch actuating member upon movement of said member within a predetermined normal range of movement to eiIect over-center movement of said switch member thereby to engage or disengage said contacts, means for biasing said switch actuating member to a position beyond said predetermined range of movement to move said switch member to a switch opening position in which over-center movement of said switch member is ineiiective to engage said contacts, and a thermally expansible member for opposing the bias of said switch actuating member and controlling movement of said switch member "within said normal range, said expansible member being arranged to hold said switch actuating member against its bias in its switch opening position within said range when said member is cooled and contracted; 5. A, thermal responsive circuit controller comprising a pair 01' cooperating switch contacts, a movable supporting and actuating member, an over-center. switch member mounted upon said actuating member and having a contact controlling portion movable with a snap action in a direction opposite to the direction of actuating expansible movement of said actuating member, thermally expansible means for controlling movement of said actuating member within a predetermined normal range of movement to effect over-center movement of said switch member and thereby to control engagement or disengagement of said contacts, and means for biasing said switch actuating member in a switch closing direction and to a position beyond said predetermined'range of movement to move said switch member positively to a position or contact disengagement wherein contact engaging over-center movemeni of said switch member with respect to said switch actuating is ineffective to engage said contacts. 1

6. A thermal responsive circuit controller comprising a pair of cooperating switch contacts, a movable switch actuating member, an overcenter switch element mounted upon said actuating member to control said contacts, said switch element comprising a pair of compression arms pivotally mounted upon said actuating member and extending in opposite directions therefrom and a tension member connected between the free ends of said compression arms, fixed stop means cooperating with said switch element to eii'ect overcenter movement of the pivoted ends of said compression arms with respect .to said tension member as said actuating member is moved within a predetermined normal range of movement. thereby to efiect engagement and disenment of said contacts, means for biasing said switch actuating member to a position beyond said normal range of movement thereby to move said switch element to a position of contact disengagement independently of the overcenter position of said switch element, said biasing means tending to effect contact engaging movement of said switch actuating member within said normal range, and a thermally expansible wire arranged normally to oppme the bias or said switch actuating member and to control movement of said member within said normal range of movement in accordance with the temperature of said wire.

7. A thermal responsive circuit controller comprising a pair of cooperating switch contacts, a movable switch actuating member, an overcenter switch element mounted upon said actuating member to control said contacts, said switch element comprising a pair of compression arms pivotally mounted upon said actuating member and extending in opposite directions therefrom and a tension member. connected between the free ends of said compression arms, fixed stop means cooperating with said switch element to effect overcenter movement of the pivoted ends oi. said compression .arms with respect to said tension member as said actuating member is moved within a predetermined normal range of movement thereby to efl'ect engagement and disengagement of said contacts, means for biasing said switch actuating member to a position beyond said normal range of movement thereby to move said switch element to a position of contact disengagement independently of the overcenter position of said element, said biasing means tending to effect contact engaging movement 01 said switch actuating member within said normal range, detent .means operable in conjunction with said switch actuating member upon movement or said actuating member beyond said normal range of movement to engage said switch element thereby positively to move said switch element to said position of contact disengagement, and a thermally expansible wire arranged normally to oppose the bias of said switch actuating member and to control movement of said member within said normal range of movement in accordance with the temperature or said wire.

8. A thermally responsive snap action circuit controller comprising a base, a fixed contact mounted upon said base, a reciprocable switch actuating member slidably mounted upon said base, an overcenter switch element carried by said actuating member and comprising a pair of compression arms pivotally mounted upon said actuating member and extending in opposite direction therefrom and a tension member connected between the free ends of said compression arms, a movable contact mounted at the free end of at least one or said compression arms, fixed stop means including said fixed contact for limit ing movement of the free ends of said compression arms, said stop means being arranged for cooperation with said actuating member to effect overcenter movement of the pivoted ends 01' said compression arms with respect to said tension member upon movement of said actuating member within a predetermined normal range of movement, thereby to control engagement of said contacts, means for biasing said actuating member to effect a contact engaging, overcenter move ment of said switch member within said normal range of movement and to move said switch member to a position beyond said normal range thereby to render overcenter movement of said switch member ineflective to control said contacts, and a thermally expansible wire arranged normally to oppose the bias of said switch actuating member and to maintain said switch actuating member positioned within said predetermined normal range of movement in accordance with the temperature of said wire.

GEORGE M. HAUSLER. 

